Dissidia had such potential. The villains, in general, were done wonderfully. Garland, in particular, was just given so much more... meat.
The heroes on the other hand... well, I found it odd that the two toughest, ballsiest, no-nonsense characters were the girl and the kid. The game took characters who in their respective games had become epically heroic and reverted them to the mindset of "I'm fighting for friendship!" It got annoying really quickly. Their journeys in Dissidia were hampered annoyingly frequently by "But, gee, what about my friends? Life is so hard!" It was laughable. Terra, on the other hand? Her biggest worry was that she would flip out and murder the fuck out of everyone.
Given, I never played Duodecim. Perhaps the characterization was improved?